MARITIME OBSERVATIONS. 309 
To remedy this, I would propofe the addition of another 
fuch L pipe, and that they fhould ftand back to back in 
the boat thus, figure 13. the forward one being worked 
as a pump, and fucking in the water at the head of the 
boat, would draw it forward while pufhed in the fame di- 
retion by the force at the ftern. And after all it fhould 
be calculated whether the labour of pumping would be 
lefs than that of rowing. A fire-engine might poflibly in 
fome cafes be applied in this operation with advantage. 
Perhaps this labour of raifing water might be fpared, 
and the whole force of a man applied to the moving of a 
boat by the ufe of air inftead of water; fuppofe the boat 
conftruéted in this form, figure 14. A, a tube round or 
{quare of two feet diameter, in which a pifton may move 
up anddown. The pifton to have valves in it, opening 
inwards to admit air when the pifton rifes; and fhutting, 
when it is forced down by means of the lever B turning 
on the center C, The tube to have a valve D, to open 
when the pifton is forced down, and let the air pafs out at 
E, which ftriking forcibly againft the water abaft muft 
puth the boat forward. If there is added an air-veflel F 
properly valved and placed, the force would continue to 
a& while a frefh ftroke is taken with the lever. The boat- 
man might ftand with his back to the ftern, and putting his 
hands behind him, work the motion by taking hold of the 
crofs bar at B, while another fhould fteer; or if he had two 
fuch pumps, one on each fide of the ftern, with a lever for 
each hand, he might fteer himfelf by working occafionally 
more or harder with either hand, as watermen now do with 
apair of fculls. There is no pofition in which the body of 
aman can exert more ftrength than in pulling right upwards. 
To obtain more f{wiftnefs, greafing the bottom of a vef- 
fel is fometimes ufed, and with good effect. I do not 
know that any writer has hitherto attempted to explain 
this. At firft fight one would imagine, that though the 
friction of a hard body fliding on another hard body, and 
Rr the 
